Mechanical properties of nanocrystalline materials

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB2) and hafnium diboride (HfB2) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre-ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine-grained ZrB2 and HfB2 have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B2O3 volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi2 improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB2 and HfB2 ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re-entry, and rocket propulsion.

Refractory Diborides of Zirconium and Hafnium

and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Nanoscaled metal borides and phosphides: recent developments and perspectives

A method for the synthesis of nearly monodisperse CuInS2 semiconductor nanocrystals (from <2 to 20 nm) was developed using generic and air-stable chemicals in a non-coordinating solvent. Such “greener” approaches also allowed the reaction temperatures to be below 200 °C. By introducing reactivity-controlling ligands for Cu, namely thiols, control of the Cu:In stoichiometric ratio in the nanocrystals was achieved. Amines were identified as catalytic reagents for the rapid oxidation of the CuInS2 nanocrystals, which could be prevented by the formation of CuInS2/ZnS core/shell nanocrystals by a one-pot approach. CuInS2/ZnS core/shell nanocrystals also showed greatly improved optical properties, with photoluminescence quantum yield up to about 30% and an emission peak position tunable from 500 to 950 nm. The versatility of the synthetic strategy was demonstrated by extending it to the synthesis of AgInS2 nanocrystals by simply replacing the copper salt by a silver salt.

Formation of high-quality I-III-VI semiconductor nanocrystals by tuning relative reactivity of cationic precursors.

A simple single-source precursor to stibnite (Sb2S3) synthesized from SbCl3 and thiourea in methanol was characterized. The thermal decomposition of the precursor in polar solvents resulted in the formation of one-dimensional Sb2S3 nanocrystallites with the growth direction along the c axis. It is found that the as-prepared Sb2S3 nanorods are formed through the spontaneous connection of adjacent particles. The pressure in the solvothermal process plays an important role in the formation of the nanorods.

Pressure-Controlled Fabrication of Stibnite Nanorods by the Solvothermal Decomposition of a Simple Single-Source Precursor

Nanocrystalline CuMS2 (M = In or Ga) were synthesized at 200 °C under solvothermal conditions by using CuCl, In or Ga, and S as reactants.

Synthesis of nanocrystalline CuMS2 (M = In or Ga) through a solvothermal process.

A direct and simple one-step hydrothermal reaction route has been developed for the synthesis of high quality trigonal selenium (t-Se) nanowires at 110 °C, with (NH4)2S2O3 and Na2SeO3 as starting materials in the presence of the surfactant sodium dodecyl sulfate (SDS). The diameter of the trigonal selenium nanowires can be tuned by carefully adjusting the initial feedstock concentration. The unusual chain like structure of the target material plays a key role in determining the final morphologies of the products. Several factors, such as initial concentration of the feedstock, the presence of surfactant, and the temperature which influences the quality of the t-Se nanowires, have been investigated. The optical properties of the t-Se nanowires with different diameters were examined by means of UV/Vis absorbance spectroscopy at room temperature. The investigation revealed that the absorbance peak for the t-Se nanowires with diameters of 20−40 nm shifts to the blue, relative to those for bulk t-Se nanowires (374 nm) and nanowires with diameters of 50−130 nm (306 nm). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Large‐Scale Synthesis of High Quality Trigonal Selenium Nanowires

Synthesis and oxidation of nanocrystalline HfB2

A new solvothermal pressure-relief (SPR) process was successfully developed for synthesis of La2O2S at relatively low temperature (300 °C) by using La(NO3)3·nH2O and NH2CSNH2 as reactants in organic media. In contrast, the normal solvothermal and hydrothermal process can only produce La(OH)CO3 and La(OH)SO4, respectively. The present SPR process provides a favorable low-temperature reaction pathway for synthesis of lanthanide oxysulfides. The mechanism and solvent effects on the formation of lanthanum oxysulfide were investigated.

Yitai Qian

Papers

Pressure-Controlled Fabrication of Stibnite Nanorods by the Solvothermal Decomposition of a Simple Single-Source Precursor

Synthesis of nanocrystalline CuMS2 (M = In or Ga) through a solvothermal process.

Large‐Scale Synthesis of High Quality Trigonal Selenium Nanowires

Synthesis and oxidation of nanocrystalline HfB2

Synthesis and Formation Mechanism of La2O2S via a Novel Solvothermal Pressure-Relief Process